1. Field of the Invention
This invention relates to a method of depicting solids of any shape and any size easily and accurately by the orthographic projection method.
2. Description of the Prior Art
With conventional depicting devices designed to sketch the shapes of solids and the surface patterns thereof by utilization of a semi-transparent mirror, depiction is effected by the center projection method by which the portion of a solid nearer the observer is depicted in larger dimensions as in photography. Therefore, the depicted shapes are distorted relative to the actual shapes of the solids, and this had led to the necessity of actually measuring the dimensions of each portion in the case of depiction of cultural objects or the like. Accordingly, such depicting devices are not so practicable for scientific use. With the orthographic projection method, as compared therewith, the scale is constant over all the surface of paper and therefore the shapes of solids and the surface patterns thereof can be expressed without distortion, and therefore a solid depicting device which can depict by such orthographic projection method has been desired.
Now, in the depicting device according to the prior art, it is the basic principle to observe a solid by one eye. This is because it is necessary to make planar the virtual image of the solid by observing the solid by one eye and to thereby make it easy to depict the solid, and because it has been considered that, with two eyes, a virtual image involving a cubic effect (three-dimensional effect) is observed to make depiction impossible.
When the virtual image of a solid is observed by two eyes with the aid of a depicting device utilizing a semi-transparent mirror, the virtual image of the solid rises and falls relative to the depicting table at a point whereat the optical path length from the observation position to the depicting table becomes substantially equal to the optical path length from the observation position to the actual solid, and so the depicting table and the virtual image of the solid can be observed as "intersecting bodies", so called in the art of drawing, by appropriately adjusting the contrast of the two. In the case, at the point of intersection between the surface of the depicting table and the surface of the virtual image of the solid, they are located at the same optical path length from the observation position. Therefore, by depicting, on the depicting table, only the point or portion of intersection between the surface of the virtual image of the solid and the surface of the depicting table while relatively decreasing or increasing the distance from the solid to the observation position, the dimensional scales of the virtual image of the solid depicted on the depicting table all become equal and it is apparent that the thus depicted image is an orthographically projected image.